fixed deepMergeObject overwriting values with undefined (#753)

feat-fix: fixed deepMergeObject overwriting values with undefined

src/util/objects.ts

@@ -51,6 +51,11 @@ export function deepMergeObject(base?: Mergeable, addon?: Mergeable): Mergeable
 
 function deepMergeObjectWithResult(addon: MergeableRecord, base: MergeableRecord, result: MergeableRecord): void {
 	for(const key of Object.keys(addon)) {
+		// values that are undefined (like from a partial object) should NOT be overwritten
+		if(addon[key] === undefined) {
+			continue
+		}
+
 		if(typeof addon[key] === 'object') {
 			if(key in base) {
 				result[key] = deepMergeObject(base[key] as Mergeable, addon[key] as Mergeable)

test/functionality/util/objects-tests.ts

@@ -116,5 +116,8 @@ describe('Objects', () => {
 				throws(true as boolean[], true as boolean[], 'lied booleans as arrays')
 			})
 		})
+		describe('with undefined', () => {
+			merged({ a: 3, b: 4 }, { a: undefined, b: 7 }, { a: 3, b: 7 }, 'do not overwrite on undefined')
+		})
 	})
 })